If you do crap on one SAC yeah its only 5% or whatever. Not a big chunk of your mark, right?
If your in a position where you've done shit on a SAC (And i know i have

) you're probably either slacking off a bit more than you should (your lazy... im guilty of this) or you dont firmly grasp or suck at the subject (im here in methods). Then again, theres the odd off chance you just messed up pretty bad on one occasion but i wouldnt put it down to this. Cold hard facts as i see em anyway.
So, back to my original line, if your doing bad in one SAC cause of some of the above factors... its probably an indication you wont do so great in the others (unless the crap mark has shown you the right way and makes you work even harder to fix your errors and study harder).
Not too cheerful is it?
[Not sure if this makes sense..its 5 am..yeah..]